Existing probes for conducting-mode atomic force microscopy (C-AFM) have disadvantages typically associated with wear of the conductive coating. For this reason, monolithic probes of metals are sometimes used, especially for long-term C-AFM experiments. However, this renders the processes difficult to scale, in particular for use on applications such as nanotechnology-based probe storage.
Existing approaches can also include electrical probe storage based on Joule heating in phase-change media, which has potential for high data rates at low cost. The phase-change medium typically used in such storage systems is the Ge2Sb2Te5 (from the chalcogenide family, commonly referred to as GST). To write bits, Joule heating of the medium by passing a current through a conducting cantilever with a nanometric tip is typically used. The heating, in turn, changes the phase of the medium from an amorphous to a crystalline state, with a corresponding change in resistivity. To read back a written bit, a simple measurement of this resistance is made, and includes a difference between the resistivities of the two states.
However, as with most c-AFM measurements, the reliability of the nanoscale tip apex conductivity, especially at the tip-sample interface, is a serious concern in commercialization. Existing conducting tips have a conductive coating that is very thin in order to minimize the tip apex radius. This coating can wear off quickly, given the high forces required for reliable conduction. Monolithic cantilevers of metals, such as tungsten and platinum, provide high current densities and fairly reliable performance at forces below the ductile deformation. However, their costs are prohibitive for any large-scale array fabrication as required for probe storage, probe-based manufacturing and other applications that require one or more probes at low cost.
Existing approaches can also include metal silicides of refractory metals such as titanium silicide. However, use of TiSi for conduction by forming TiSi on a silicon wafer results in an oxide forming on the surface (as evidenced by the presence of the breakdown voltage), which impeded conduction.
As such, it would be advantageous to create an electrical probe storage based on conducting cantilevers, as well as to enable reliable conduction using C-AFM tips for materials characterization and manipulation and reliable conduction for applications on probe-based lithography.